Sofa



FIG. 1 is a is a front elevational perspective view of the sofa design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a right, side view thereof; and,

FIG. 5 is a back view thereof.

The broken line disclosure is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a sofa, as shown and described. 